This invention relates to a controlled directional drilling tool.
Holes are drilled into coal beds or rock beds for the purpose of withdrawing entrapped gases, surveying the earth's crust, etc. In the course of such drilling, there may arise necessity for changing the direction of drilling by reason of geological conditions or drilling conditions.
When there arises necessity for changing the direction of drilling while the drilling is in progress it has been customary to effect the required change by drawing the drilling tool out to the surface, separating the drill pipe and the drill bit, then re-joining them through the medium of a sub bent by the angle required for the control of the drilling direction and resuming the drilling operation.
U.S. Pat. Nos. 2,796,234 and 2,891,769 disclose directional drilling tools. The tool of the former disclosure is based on a method such that required directional drilling is obtained by hydraulically causing arms and rollers to protrude to a controlled extent from a drill pipe. The tool of the latter disclosure has a drill pipe provided at separated levels with two guide means each consisting of four guide runners, whereby required control of the drilling direction is accomplished by causing the individual guide runners to protrude from their respective resting position to extents controlled by suitable hydraulic means.
In these directional drilling tools, however, the hydraulic pressure for causing the revolution of the drill bit and that for effecting the protrusion of arms, rollers or guide runners issue from a common source. Consequently, the hydraulic systems in the tools are inevitably complicated. Further, since the arms, rollers or guide runners always protrude from the surface of the drill pipe, they tend to sustain damage where the holes drilled by the tools happen to be small in diameter. Moreover, because of the existence of such protruding articles there is not only the possiblity of malfunction but the danger of the preventing bending when it is desired and inducing bending when it is not desired.
An object of the present invention is to provide a controlled directional drilling tool which permits the direction of drilling to be changed certainly to a new desired direction by an extremely simple mechanism.